http://www.cyberforum.ru/attachments/70241d1301661028

...
if (y<=0) and (x<=0) and (y<=sqrt(sqr(r)-sqr(x)) or
  (y>=sqr(x-1)) and (x>=0) and (y<=sqrt(sqr(r)-sqr(x)) then
  writeln('yes')
   else writeln('no');
...